Question:

An optimistic model for a battery is just an ideal seat of EMF. A further realistic model commonly used to model actual batteries is

Answer:

Note that the internal resistance in sequence with the ideal seat of EMF is still a model. The battery both preserves a potential difference and provides resistance to any charge that may flow through it. Although the two effects in practice cannot be separated from each other. The complete material of the battery contributes to the resistance. The battery just acts similar to a resistor in series with an ideal seat of EMF. A battery can certainly not physically be separated into a resistor and an ideal seat of EMF.